If you can’t manage to be original, at least put the familiar in a different package. That applies to “Ringer” (8 p.m., CW), a new head-scratcher drama starring Sarah Michelle Gellar. If we were pitching this idea in Hollywood, we’d call it “Nikita” meets “The Patty Duke Show.”

Gellar plays Bridget, a troubled former hooker and exotic dancer six months sober who’s landed in protective federal custody so she can testify against a shadowy figure from an Indian reservation crime syndicate. Her FBI handler, Agent Victor Machado (Nestor Carbonell of “Lost”), assures her safety, but anybody who has seen Frankie Five Angels’ last scene in “The Godfather Part II” knows she’s in trouble.

On the eve of her big testimony, Bridget escapes to New York to reunite with her estranged twin, Siobhan Martin (also played by Gellar). They meet on a speedboat and “talk” to each other via some pretty shaky special effects. Given that she’s not the drunk, slutty sister wanted by the FBI and pursued by a desperate killer, Siobhan seems distinctly unhappy. And wouldn’t you know it, moments later she vanishes, presumably at sea and apparently by her own hand.

Ever the improviser, Bridget “vanishes” by posing as her twin. But wait a minute. Won’t Siobhan’s rich husband notice something different? Luckily for Bridget-turned- Siobhan, she and her dashing hubby Andrew Martin (Ioan Gruffudd, “Fantastic Four”) aren’t exactly intimate. And as the ruse continues, Bridget discovers new and weird details about her sister’s sham marriage, her affairs, her not-so-best friend and so much more.

Best known for her witty and assured delivery in “Buffy the Vampire Slayer,” Gellar has to spend a lot of time here acting wide-eyed and confused. And who can blame her? But if she and “Ringer” ever find their moorings, this has the potential to be a real over-the-top guilty pleasure.

I’m reminded of “Dead Ringer,” one of Bette Davis’ best/worst movies. In that 1964 hoot, she plays a twin who kills her sister and assumes her posh existence, only to go up the river for killing “herself”!

”Ringer” also has the fun, sleazy feel of the dearly departed “Dirty Sexy Money,” a soapy ABC show that made you pity the rich for their miserable, complicated lives while admiring their apartments, decor and wardrobes.

• Just when you think you’ve heard everything, “Jacqueline Kennedy: In Her Own Words” (8 p.m., ABC) airs.

Tonight’s other highlights

• Postgraduate options loom on the fourth season premiere of “90210” (7 p.m., CW).

• The final four perform on “America’s Got Talent” (8 p.m., NBC).

• “Frontline” (8 p.m., PBS) presents “The Interrogator.”

• Sarah’s 40th hits hard on the season premiere of “Parenthood” (9 p.m., NBC).

• “POV” (9 p.m., PBS, check local listings) presents the documentary “If a Tree Falls: A Story of the Earth Liberation Front.”

• The club faces a major decision on “Sons of Anarchy” (9 p.m., FX).